3. Stock market losers -- Monsanto, Gilead: Shares in both Monsanto(MON) and Gilead Science(GILD) are declining by about 2% premarket.

Monsanto shares are dipping after a World Health Organization agency published a research paper saying the firm's weedkiller Roundup probably causes cancer. Monsanto countered the claims, saying its products are safe and meet regulatory standards. The company also said the report conflicts with findings from other WHO agencies.

Shares in Gilead Sciences are expected to open in negative territory after the company reportedly sent an email to healthcare workers warning that patients taking its hepatitis C drug could be at risk of serious heart problems if they are also taking another type of heart medication.

Tsipras has warned Merkel that it will be "impossible" for Greece to pay its debts in the coming weeks without further financial assistance from Germany and its international partners. Europe wants Greece to deliver on promised reforms before releasing any more funds.

The meeting comes after a video emerged this month showing Greece's outspoken finance minister Yanis Varoufakis making a lewd gesture directed towards Germany. The video was taken in 2013, before Varoufakis was installed in his new job.